I'd suggest you get a bigger, better monitor first, the HD5770 in your sig is plenty for 1680x1050 and can play most games at 1920x1200 as long as you keep the AA low or off (mine could run Crysis at 'high' on a modestly overclocked C2D E6600).
here is a way to make crysis run much better, you might or not know this, the graphics will remain almost the same,
search it online i dont have time to explain but basically after the target box in the shortcut to play crysis/ or warhead add -dx9:
"C:\Program Files (x86)\Crysis Warhead\Bin32\Crysis.exe" -dx9
on my 4850 at 1680 by 1050 I played on dx9 on very high at almost 30 fps constantly with a q6600 at 3.0ghz
the difference in crysis for dx9 and dx10 is minimal and not worth the performance loss (unplayable for me in dx10)
also note in the original crysis when you do this the very high options are greyed out, so all you gotta do is go in the files and replace the high parameters with very high and then when you select high in game it will be like selecting very high.